A device that uses an electrochemical reaction, for example, a solid oxide fuel cell (hereinafter, referred to as SOFC) may be usefully used as a mobile-type or stationary-type power generation device because the device does not release environmentally harmful gases. In general, a high-temperature fuel cell such as a solid oxide fuel cell can use various types of fuels including a hydrocarbon such as methane and/or carbon monoxide because the fuel cell requires a high operating temperature to obtain sufficient oxygen ion conductivity through an oxide-based membrane. In order to produce hydrogen in-situ from these carbon-containing fuels, external or internal steam reforming processes have been widely used.
However, the steam reforming system reduces the efficiency because the system needs to store and supply water from the systematic point of view.
Meanwhile, numerous studies in which bio gas is used as a fuel have been recently conducted. A bio gas that can be obtained from biomass can be converted into synthetic gases (H2+CO) through methane dry reforming or bio gas reforming [hereinafter, referred to as ‘dry reforming’]. For reference, a major constituent of the bio gas is methane (50 to 60 mol %) and carbon dioxide (40 to 50 mol %). In the dry reforming system, water in the steam reforming is replaced with carbon dioxide. Since the dry reforming directly injects a bio gas of the methane and carbon dioxide without a need for any separate device, the systematic efficiency may be increased, and a compact SOFC system design with an improved efficiency may be possible.
However, since a carbon source is increased on the whole in the dry reforming method as described above, the dry reforming method cannot help but be vulnerable to carbon deposition or deactivation via carbon coking as compared with the steam reforming using water.
Explaining more theoretically, carbon dioxide is less reactive to carbon removal through formation of carbon monoxide (CO2+C->2CO: reverse Boudouard reaction), so that the dry reforming method cannot help but be very sensitive to deactivation via carbon coking or carbon deposition unless steam is added. That is, when a bio gas is directly injected, a thermodynamically more favorable carbon coking occurs based on the C—H—O ternary diagram.
Considering these circumstances, in order to improve the efficiency of the entire system, developing a durable catalyst that may be used in all the reforming reactions which accompany carbon coking and optimizing a fuel composition having an oxygen source (for example: oxygen or water) for preventing carbon deposition are required